But the calculation doesn’t quite add up because you’re calculating with a constant interest rate. With an annuity loan, it already decreases from month 2 onwards, and so do the interest payments. The theoretical savings are therefore smaller and decrease even further in the following years.
The calculation is simplified, which is why I wrote “roughly calculated.” Since the building savings contract is usually paid off faster than an annuity loan, the interest advantage even increases. You just have to make sure when calculating that the total installment remains comparable.
But as you correctly pointed out, the interest earnings in the building savings contract are not taken into account. Although a processing fee is deducted, with only 1.5% that still amounts to €115. Of the calculated €125, only €10 remain. From year 2 onwards, it probably no longer pays off because the credit interest increases and the loan interest decreases.
If you want to calculate precisely, then also take into account capital gains tax + solidarity surcharge on the credit interest. Furthermore, the effect improves due to the different repayment rates in the following years, not worsens.
But your entire calculation is a naive calculation since you assume that the original poster needs €15,000 less loan. But he already has €7,300 in the building savings contract, which remains as credit balance, whereas you fully include this in your "combo package" and take out only €7,700 additionally. So you compare a loan of €380,000 (1.75% + 4.25%) with a loan of €387,700 (1.8%).
No, I always calculate with €380,000. Either €380,000 loan and then keep credit interest on the building savings balance of €7,300, or €365,000 + €15,000 (of which €7,300 is credit balance and €7,700 financing).
There is a third option: having the balance paid out and then borrowing €7,300 less. If the loan-to-value threshold is undercut by the €7,300, then this is probably the most sensible option.
However, I wanted to illustrate with my calculation that under certain circumstances even the building savings loan can make sense.
If the loan interest rate can of course be reduced significantly, then it will inevitably become attractive at some point. For us, the jump from full financing to 85-90% (depending on the bank) was quite large. Under 80% there wasn't much left.
Exactly that was my intention to show that even only a 0.05% interest improvement improves the overall financing, although you have to pay over 4% for the building savings loan. The greater the interest improvement, the more sensible the option is.